In recent years, when an electrophotographic process is applied to form images, downsizing of toner particles is promoted in order to attain higher image quality, and a polymerized toner is manufactured to meet this demand. This polymerized toner is composed of resin particles prepared by conducting a polymerization process via emulsion polymerization and the like, colorant particles, and toner particles acquired by coagulating other particles as a toner composition if desired. After oil droplets are formed by dispersing a polymerizable monomer raw material in an aqueous medium, used subsequently to incorporate an emulsifier, the resin particles to acquire a polymerized toner were conventionally prepared via emulsion polymerization in which radical polymerization was conducted via oil droplets by adding a polymerization initiator. A styrene-acryl based resin particles exemplified, for example (refer to Patent Document 1 and Patent Document 2, for example).
Since kinds of polymerizable monomers used for radical polymerization are limited in such a toner manufacturing method, the resulting toner, however, is limited to toner particles composed of vinyl based resin particles or acryl based resin particles.
Since in the case of polyester resin, a toner exhibits excellent fixability obtained by excellent viscoelasticity of the polyester resin, a toner composed of toner particles containing coagulated polyester resin particles is desired. In order to acquire a toner containing such polyester resin particles, a solution in which the polyester resin is dissolved in an organic solvent is dispersed in an aqueous medium, and these polyester resin particle-to-polyester resin particle are subsequently coagulated with colorant particles, whereby toner particles can be prepared via solvent removal. This toner manufacturing method is exemplified (refer to Patent Document 3, for example). On the other hand, in the case of toner formed by toner particles made only of a polyester resin, an off-setting phenomenon is possibly generated with no sufficient releasing capability in a fixing process, whereby it is well-known, for example, that high releasing capability can be obtained by adding wax as a releasing agent into the polyester resin constituting toner particles
It is, however, difficult to evenly disperse wax in the polyester resin, resulting in reducing the toner charging amount largely since a phenomenon of releasing wax from formed toner particles is generated, whereby the released wax is shifted to a carrier in the case of a two-component developer, and is also shifted to a developing sleeve in the case of a single-component developer. Particularly in the case of an image forming method to form color images by superimposing plural toner images employing color toner, color reproducibility is largely lowered via slight variation of the developing toner amount caused by a very small change of the charging amount.
The reason why it is difficult to evenly disperse wax in the polyester resin, though considered to be less certain, is that wax and a polyester resin are presumably phase-separated since wax is basically a material containing a nonpolar group such as a long-chain hydrocarbon group and so forth in the molecule, whereas a polyester resin is a material containing a number of polar groups such as an ester group and so forth in the molecular chain, in the case of employing a commonly known method, for example, of forming particles via pulverization after melting and kneading wax and a polyester resin, or forming particles via deliquoring after dispersing in the aqueous medium wax and a polyester resin which are dissolved in a cosolvent.
(Patent Document 1) Japanese Patent O.P.I. Publication No. 2000-214629
(Patent Document 2) Japanese Patent O.P.I. Publication No. 2001-125313
(Patent Document 3) Japanese Patent O.P.I. Publication No. 2004-109848